пятница, 29 декабря 2017 г.

Neptunite While it was first discovered in the Narssârssuk…


While it was first discovered in the Narssârssuk pegmatite of western Greenland in 1893 (see http://bit.ly/2l1TNFb), most of the beautiful specimens on the market originate in the Benitoite mine of California in association with a white natrolite matrix (see http://bit.ly/2BTPO84), though the 6.7 x 1.7 x 1.2 cm whopper in the photos is what mineral people call a floater, a crystal that grew in a cavity without being attached to the matrix or country rock wall. This saves on preparation and makes extraction easy, many specimens on the market have had the matrix removed with acids to expose the crystals.

It was named after the Roman god of the sea, due to its geological association with and similarity to the mineral Aegirine, named after the Viking sea deity. Colour is usually black, through brown and maroon specimens exist. With a Mohs hardness of 5-6 it has been faceted for collectors on occasion. The Benitoite mine bears witness to high pressure metamorphism in the long standing subduction zone whereby several oceanic plates have plunged into the mantle at the Western edge of the growing North American continent followed by alteration by deep Earth fluids. Other localities include the Mont St Hilaire mine in Quebec and the Kola Peninsula of Russia.


Image credit: Rob Lavinsky/iRocks.com





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Соединение Юпитера  ♃  и  Сатурна  ♄   21 декабря 2020   16 : 30 по Гринвичу, 21 декабря 2020 года, состоится условное соединение Юпитера ♃ ...